Apparatus for testing the tensile strength of sheet material

ABSTRACT

The apparatus includes a pair of upstanding support members, each mounting clamps adapted to be in a position juxtaposed to each other, and the support members are mounted in pivotal relation one to the other. Hydraulic devices are provided for adjusting the clamping pressure on the sheet material to be tested, and a pneumatic device is provided for forcing the clamps away from each other to break the sheet material.

United States Patent Cowan [451 Dec. 26, 1972 [54] APPARATUS FOR TESTING THE TENSILE STRENGTH OF SHEET MATERIAL Wavell Frederick Cowan, 36 Parkside, Montreal, Quebec, Canada Filed: April 20, 1971 Appl. No.: 135,733

Inventor:

US. Cl ..'..73/95, 73/103 Int. Cl. ..co1n-3/10 Field of Search ..73/95, 103, 95.5

[56] References Cited UNITED STATES PATENTS 3,530,709 9/1970 Nemeth ..73/95 3,559,469 2/1971 Stonebridge ..73/95 2,563,881 8/1951 Steadman ..73/95 3,318,142 5/1967 Shoemaker ..73/95 Primary Examiner-Jerry W. Myracle Attorney-Alan Swabey [5 7] ABSTRACT The apparatus includes a pair of upstanding support members, each mounting clamps adapted to be in a position juxtaposed to each other, and the support members are mounted in pivotal relation one to the other. Hydraulic devices are provided for adjusting the clamping pressure on the sheet material to be tested, and a pneumatic device is provided for forcing the clamps away from each other to break the sheet material.

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IN VENTOR Wuvell F. COWAN PATENT ED "E625 I973 3. 707, l 19 saw 3 or 3 INVENTOR Wavell F. COWAN A TTORNEY APPARATUS FOR TESTING THE TENSILE STRENGTH OF SHEET MATERIAL BACKGROUND OF INVENTION 1. Field oflnvention The present invention relates to an apparatus for testing the tensile strength of sheet material and in particular fibrous sheet material such as paper.

2. Description of Prior Art In testing the tensile strength of paper sheets, certain problems are encountered in view of the particular construction of the paper. For instance, sheet paper is made up of a mat of fibers, the fibers being held together by inter-fiber bonds. Therefore, in using conventional tensile strength testing equipment whereby sheet material is held between spaced-apart opposed pairs ofjaws the sheet of paper can fail due to failure of the inter-fiber bonds rather than due to a failure of the fibers and, therefore, the actual tensile strength of the fibers is not really tested. It has since been found that in order to properly test the tensile strength of fibers in a particular sheet of paper it is necessary to obtain zerospan, that is, when the opposed clamping jaws are contacting each other and the space between the opposed clamping jaws is practically nil. Thus, the opposed pairs of clamping jaws should theoretically be clamping the same fibers.

SUMMARY OF INVENTION It is an aim of the present invention to provide an efficient and reliable apparatus for testing the tensile strength of sheets of paper at zero-span conditions.

It is a further aim of the present invention to provide clamping jaws in which the pressure applied by the clamping jaws to the sheet of paper can be properly controlled so as to avoid damaging the sheet of paper by excessive pressures applied to the clamping jaws, while at the same time providing adequate clamping pressure to prevent slippage of the paper during tensile testing.

Generally, the apparatus in accordance with the present invention includes pairs of opposed clamping jaws for clamping the sheet at separate adjacent areas; and means for mounting one of the pairs of clamping jaws for pivotal movement relative to the other and means effecting said pivotal movement.

More specifically, an apparatus according to the present invention for testing the tensile strength of fibers in a flat sheet comprises pairs of opposed clamping jaws wherein each pair ofjaws is adapted to'engage between them a portion of the sheet material adjacent that portion gripped by the opposed pair of jaws. Means are provided for controlling the pressure of each pair of clamping jaws on the sheet material. Means are also provided for pivotally mounting one of the opposed pairs of clamping jaws relative to the other for pivotal movement between a first position whereby the opposed pairs of clamping jaws are in close proximity in contact with each other and a position spaced apart from each other with the clamping jaws still gripping portions of the sheet. Means are also provided for causing the pivotal movement of one pair ofjaws relative to the other, said means includes a fluid-operated piston and cylinder arrangement connected between the opposed pairs ofjaws whereby a fluid load in the cylinder causes the opposed pairs of jaws to move away from said first position when the fluid load has overcome the tensile strength of the sheet gripped by the opposed pairs ofjaws. Means are also provided for recording the fluid load required to overcome the tensile strength of the sheet material whereby the tensile strength of the sheet material-can be conventionally measured.

BRIEF DESCRIPTION OF THE DRAWINGS I view of the detail of the apparatus shown in FIG. 2;

FIG. 6 is a horizontal cross section taken along lines 6-6 of FIG. 2;

FIG. 7 is a vertical cross section taken along lines 7- 7 of FIG. 2;

FIG. 8 is an enlarged detailed view of a detail shown in FIGS. 2 and 7; and

FIG. 9 is a vertical cross section taken along lines 9- 9 of FIG. 2.

Referring to the drawings and particularly to FIG. 1, the apparatus is shown having a base 10 with a control panel 12 on the front part of the base 10. Two support members 14 and 16 extend upwardly from the rear part of the base. Each support member mounts a clamp head 18 and 20, respectively. Clamp 22 is provided with the clamp head 18 and a clamp 24 provided with the clamp head 20. Piston and cylinder arrangements 26 and 28 are mounted to the support members 14 and 16 respectively and move the clamps 22 and 24 by means of the levers 27 and 29. In the present embodiment, the support frame member 16 is fixed to the base, while the support member 14 is pivotally mounted to the support member 16.

As shown in FIGS. 2 and 9, the support member 14 is pivoted by means of a spring plate 32- fixed at one end to the support member 16 by means of screws 34. Spaced above the screws 34, there is a fulcrum bar 36, having a triangular cross section which abuts against the spring plates 32 and is held there by means of screws 38.

Finally, the support member 14 is fixed to the other end of the plate 32 by means of screws 40. As shown in FIG. 2, a recess 42 is provided in the support member 16 in order to receive the head of screws 40.

Referring now to FIGS. 2 through 8, the clamping heads 18 and 20 include an anvil 44 and 46 secured to the top of each support member 14 and 16, respectively. The anvils are fixed to the tops of the frame members by means of screws 48. The rear portion of the support members 14 and 16 extend upwardly in upstanding members 50 and 52, respectively, with each upstanding member 50 and 52 having a machined, vertical surface 51 and 53, respectively. Side plate 54 and 56 extends at right angles from the upstanding members and 52, respectively, as shown in FIG. 3. The side members 54 and 56 are also provided with machined surfaces which are exactly at right angles to the surfaces 51 and 53. The clamps 22 and 24 include sliding clamp jaw members 58 and 59, respectively, having contact surfaces adapted to slide in vertical planes along the machined surfaces 51 and S3, respectively, and the machined surfaces of the side plates 54 and 56.

As shown in FIG. 5, the pairs of jaws 44 and 58 and 46, 59 are shaped so that they will grip the paper close together and having a span therebetween approaching zero. The jaws are stepped as shown so that only a small concentrated portion of the paper is gripped.

Finally, a cover 60 and 62 is provided about the ope sides of the clamping heads 18 and 20. Adjustment screws 64 are provided for bearing the sliding jaw members 58 and 59, against the sliding surfaces of the upstanding members 50 and 52 and the side plates 54 and 56.

Each jaw member 58 and 59 includes a recessed portion in which there is provided a spring 74 and 76 respectively. The spring 74 and 76 abut against projections and 72 extending from the upstanding members 50 and 52. This can be seen more clearly in FIGS. 7 and 8.

The levers 27 and 29 as shown in FIG. 2 pivot in recesses 66 and 68 of the side plates 54 and 56, respectively. Recesses are formed in such a way that they present a sharp edge where the levers 27 and 29 are pivoted. The levers 27 and 29 are provided with V- shaped notches 78 and 80 which engage a sharp edge formed by the recesses 66 and 68 respectively. Finally, adjustable pressure members 82 and 84 are provided on the levers 27 and 29,'respectively, and these in turn press against the top surfaces of the sliding top clamp members 58 and 59, respectively. Of course, the levers 27 and 29 are connected by means of pivot brackets 86 and 88, respectively, to piston rods 90 and 92. These piston rods form part of the cylinder piston arrangement 26 and 28, respectively. The cylinders thereof are pivotally mounted to cylinder brackets 94 and 96 secured to the side surfaces of the support members 14 and 16, respectively.

A recess 98 is provided in the upper portion of the support member 16 and is covered by a cover plate 106. A piston rod 100 connected to the support member 14 extends through a passage into the recess 98 and mounts a piston head 102. Finally, a diaphragm 104 which is secured peripherally by the cover plate 106 is attached to the piston head 104. The cover side of the cavity so formed is connected to a suitable compressed air source (not shown).

The support bracket 14 is provided with a passage 108 and a rod 110 which is fixed at the one end to the support member 16 extends through the passage 108. On the 'free end of the rod 110 is a resilient stop member 112.

In the present embodiment, the support member 14 is shown with large openings therein which is merely to lighten the support member 14.

In operation, when it is required to test the tensile strength of a piece of sheet material, especially fibrous material, such as paper, the sample sheet material is placed spanning the anvils 44 and 46 which are juxtaposed as shown in FIGS. 2 and 5.

When the apparatus is in a position of rest, the piston rods 90 and 92 of the piston and cylinder arrangements 26 and 28 are in their extended position with the levers 27 and 29 at an upward angle as represented by the dotted lines in FIG. 2. In that position, the springs 74 and 76 acting against the projections 70 and 72 lift the top sliding clamps 58 and 59 so that they are spaced apart from the anvil surfaces 44 and 46. Therefore, in such a position, easy access is had to the clamps 22 and 24, for placing the sample test paper as described above.

The on-off switch 114 on the control panel is then flicked, thus opening a conventional hydraulic circuit to the piston and cylinder arrangements 26 and 28 causing the piston rods 90 and 92 to retract within the cylinders. This causes the levers 27 and 29 to pivot to their downward position as shown in FIG. '2, thereby forcing the sliding jaw'members 58 and 59 to move downwardly towards the anvils 44 and 46, respectively. The amount of pressure which is required to hold the sample test paper is controlled by means of a hydraulic regulator which in turn is activated by the regulator knob 1 16 on the control panel 12. The amount of pressure is recorded on the dial 1 18.

Once the clamp members 58 and 59 engage the test paper against the anvils 44 and 46, a load pressure push button is depressed to allow compressed air, or other elastic fluid, into the cover-side of cavity 98. The pressure will build up in the right-hand side of the cavity 98 until it overcomes the tensile strength of the test paper; at this point, the piston head 102 and piston rod 100 connected to the support member 14 will force the support member to move away from the support member 16 about the axis of the fulcrum bar 36. The pivotal movement of the support member 14, however, will be limited by means of the stop member 112 on the rod 110. Once the test has been completed, a reading of the amount of pneumatic pressure required to break the paper has been recorded from the gauge 124, the

push button 122 is depressed, thereby releasing the pneumatic pressure in the cavity 98. Of course, the support member 14 will then pivot back to its home position juxtaposed with the support member 16 by means of the spring plate 32.

lclaim:

1. An apparatus for testing the tensile strength of sheet material comprising pairs of opposed clamping jaws wherein one pair of jaws is adapted to grip a portion of the sheet material and another pair of jaws adapted to engage an adjacent portion of the sheet material; means for pivotally mounting one of the opposed pairs of clamping jaws relative to the other between a first position whereby opposed pairs of clamping jaws are juxtaposed in contact with each other and a position spaced apart from each other with the clamping jaws still gripping the portions of the sheet.

2. An apparatus as defined in claim 1, wherein there are two pairs of clamping jaws and each pair is mounted on a first and a second supporting member respectively, the first supporting member being mounted to a base and the second supporting member is pivotally mounted to the first supporting member such that in a first position, the two pairs of clamping jaws are juxtaposed, and means are provided for opening and closing each pair of jaws for receiving a piece of sheet material to be tested.

3. An apparatus as defined in claim 2, wherein a piston and cylinder arrangement is provided on each supporting member to open and close each pair ofjaws.

4. An apparatus as defined in claim 3, wherein each pair of jaws on each supporting member includes a fixed bottom surface and a top jaw adapted for sliding movement along an axis normal to the plane of the bottom surface and said piston and cylinder arrangement being connected to the top sliding jaw.

5. An apparatus as defined in claim 3, wherein the piston and cylinder arrangement for moving the sliding clamp jaw is mounted to the side of the support means is connected to a lever arm pivotally mounted adjacent the sliding jaw, whereby the lever contacts the sliding jaw.

6. An apparatus as defined in claim 2, wherein the means effecting the pivotal movement of the second supporting member from the first supporting member includes a piston and cylinder arrangement provided between the first and second supporting member and adapted to receive pneumatic fluid under pressure.

7. An apparatus as defined in claim 1, wherein the means for effecting the pivotal movement of the pairs of clamping jaws includes a piston and cylinder arrangement provided between the pairs of clamping jaws and adapted to receive an elastic fluid for effecting the pivotal movement between the opposed pairs of jaws.

8. An apparatus for testing the tensile strength of sheet material comprising pairs of opposed clamping jaws wherein each pair of jaws is adapted to engage between them a portion of a sheet material adjacent that portion gripped by the opposed pairs of jaws; means controlling the pressure of each pair of clamping jaws on the sheet material; means for pivotally mounting one of the opposed pairs of clamping jaws relative to the other between a first position whereby opposed pairs of clamping jaws are in close proximity in contact with each other and a position spaced apart from each other with the clamping jaws still gripping portions of the sheet; means for causing the pivotal movement of one pair of jaws relative to the other, said means including a fluid operated piston and cylinder arrangement connected between opposed pairs of jaws whereby the fluid load of the cylinder causes the opposed pairs of jaws to move away from said first position when the fluid load has overcome the tensile strength of the sheet gripped by the opposed pairs of jaws and means are provided for recording the fluid load required to overcome the tensile strength of the sheet material. 

1. An apparatus for testing the tensile strength of sheet material comprising pairs of opposed clamping jaws wherein one pair of jaws is adapted to grip a portion of the sheet material and another pair of jaws adapted to engage an adjacent portion of the sheet material; means for pivotally mounting one of the opposed pairs of clamping jaws relative to the other between a first position whereby opposed pairs of clamping jaws are juxtaposed in contact with each other and a position spaced apart from each other with the clamping jaws still gripping the portions of the sheet.
 2. An apparatus as defined in claim 1, wherein there are two pairs of clamping jaws and each pair is mounted on a first and a second supporting member respectively, the first supporting member being mounted to a base and the second supporting member is pivotally mounted to the first supporting member such that in a first position, the two pairs of clamping jaws are juxtaposed, and means are provided for opening and closing each pair of jaws for receiving a piece of sheet material to be tested.
 3. An apparatus as defined in claim 2, wherein a piston and cylinder arrangement is provided on each supporting member to open and close each pair of jaws.
 4. An apparatus as defined in claim 3, wherein each pair of jaws on each supporting member includes a fixed bottom surface and a top jaw adapted for sliding movement along an axis normal to the plane of the bottom surface and said piston and cylinder arrangement being connected to the top sliding jaw.
 5. An apparatus as defined in claim 3, wherein the piston and cylinder arrangement for moving the sliding clamp jaw is mounted to the side of the support means is connected to a lever arm pivotally mounted adjacent the sliding jaw, whereby the lever contacts the sliding jaw.
 6. An apparatus as defined in claim 2, wherein the means effecting the pivotal movement of the second supporting member from the first supporting member includes a piston and cylinder arrangement provided between the first and second supporting member and adapted to receive pneumatic fluid under pressure.
 7. An apparatus as defined in claim 1, wherein the means for effecting the pivotal movement of the pairs of clamping jaws includes a piston and cylinder arrangement provided between the pairs of clamping jaws and adapted to receive an elastic fluid for effecting the pivotal movement between the opposed pairs of jaws.
 8. An apparatus for testing the tensile strength of sheet material comprising pairs of opposed clamping jaws wherein each pair of jaws is adapted to engage between them a portion of a sheet material adjacent that portion gripped by the opposed pairs of jaws; means controlling the pressure of each pair of clamping jaws on the sheet material; means for pivotally mounting one of the opposed pairs of clamping jaws relative to the other between a first position whereby opposed pairs of clamping jaws are in close proximity in contact with each other and a position spaced apart from each other with the clamping jaws still gripping portions of the sheet; means for causing the pivotal movement of one pair of jaws relative to the other, said means including a fluid operated piston and cylinder arrangement connected between opposed pairs of jaws wheReby the fluid load of the cylinder causes the opposed pairs of jaws to move away from said first position when the fluid load has overcome the tensile strength of the sheet gripped by the opposed pairs of jaws and means are provided for recording the fluid load required to overcome the tensile strength of the sheet material. 